"Operationally, we're at the same level as when US Secretary of State Condoleezza Rice visited Athens (last year)," public order ministry spokesman Panagiotis Stathis told AFP.

"But as sports events go, this is definitely the largest since the Games."

Around 7,500 officers have been specifically detailed to security operations related to the Champions League final, but the city's entire 15,000-strong police force will be on alert, Stathis said.

Police will form three control zones around the Olympic Stadium to regulate incoming fans and search for weapons, banned items such as offensive banners, and fake tickets.

They also plan to use colour pellets to brand troublemakers, a measure never before taken in Greece, a police source said.

Two years ago, Liverpool and Milan met at the Champions League final in Istanbul without major incident, and Greek police are loath to see a precedent start now.

"Milan fans we know, the team has played here in the past and created no problems in Istanbul...plus there is no open vendetta between Milan and Liverpool supporters," Stathis said.

The two clubs have received 34,000 tickets for their supporters, but the total number of fans travelling to Athens for the final -- initially estimated by Greek police at 50,000 -- is unclear.

Another 29,000 tickets were made available to national football federations, sponsors, guests of European governing body UEFA and by open ballot.

Many of these tickets have already been traded online at prices reaching up to ten times their value, from an official price of 80, 140 and 200 euros (108-270 dollars) to between 830 and 1,900 euros (1,125-2,600 dollars).

Fans with tickets will be escorted by police directly to the Olympic Stadium, while the remainder will be permitted to circulate freely around Athens but will have their movements shadowed by riot police.

"This is normally a disadvantage, but the fact that Athens has no large boulevards will make it easier to monitor the fans," Stathis said. "In any case, we cannot prevent people from travelling to support their club."

In order to minimise fan movement, the police have asked hoteliers around town to show the match -- aired on state television NET -- on large screens in their bar and restaurant areas.

"The point is to create a stadium atmosphere," the ministry spokesman said.

To prevent a chance encounter between the two teams' supporters, Liverpool fans will be forwarded to the Olympic Stadium on buses whilst Milan fans will travel on the suburban railway.

Fans will also be given coloured bracelets upon landing at Athens International Airport to help staff escort them back in separate groups.

In total, 100 charter flights from Britain and 80 flights from Italy will arrive in Athens until May 24, in addition to regular flights and 106 private jets carrying VIP guests.

The Liverpool and Milan squads arrived on Monday.

In addition to planning the security operation, Greek police brass are in last-minute talks to prevent police unionists from staging a demonstration in Athens on the day of the final to pressure the government on salary increases.

"This mobilisation must not be held...it could blemish this great sporting event and embarrass our country internationally," said Public Order Minister Vyron Polydoras.

The union has pledged not to disrupt security plans, with only off-duty officers set to participate in the protest.